Encoder system for position determination with varying scale

ABSTRACT

By configuring an encoder scale as a varying scale with successively increasing or decreasing pitch, sensors in a travel path of the scale can detect a phase difference to determine an absolute position of the scale for use in an industrial control system. Due to the successively increasing or decreasing pitch, each sensor can detect successively increasing or decreasing properties (such as magnetic fields) from the scale in a uniquely identifiable pattern. By taking the difference between readings of adjacent sensors, each sensor detecting properties of the scale, an absolute position of the scale between the sensors can be determined. The principle for feedback for the encoder system is analogous to a Nonius or Vernier principle to determine absolute position.

FIELD OF THE INVENTION

This application claims priority to U.S. patent application Ser. No.15/992,935, entitled “Encoder System for Position Determination withVarying Scale,” filed on May 30, 2018, which is herein incorporated byreference.

FIELD OF THE INVENTION

The subject matter disclosed herein relates generally to industrialcontrol systems, and more particularly, to an improved encoder systemfor position determination in an industrial control system.

BACKGROUND OF THE INVENTION

In industrial control systems, it is often desirable to move objectsfrom one location to another for accomplishing various tasks. Forexample, rolling conveyors are often used to move objects from onelocation to another for interacting with different machines of anindustrial control process, such as a first machine at a first locationfor placing a box, a second machine at a second location for filling thebox, and a third machine at a third location for closing the box.

More recently, a track system has been developed in which multiple“carts” can be independently driven along a “track” for accomplishingthe various tasks of the industrial control process. By providingindependently controllable carts, the timing of each task can be moreprecisely controlled than traditional systems such as rolling conveyors.

In such track systems having moving carts, it is often desirable to knowthe position of each cart at all times, including during power-up, toensure that the industrial control process is executing correctly. Toaccomplish this, each cart can be configured with an encoder scale, suchas a magnetic scale, and the track can be configured with arrays ofsensors, such as magnetic sensors, with an air gap between the encoderscale and the sensors. In operation, when an encoder scale on a movingcart is near a group of sensors on the track, the sensors can determinethe absolute position of the cart by measuring the varying magneticfield strength or varying magnetic field angle from the magnetic encoderscale on the cart. Conversely, when the cart is away from the group ofmagnetic sensors on the track, the magnetic sensors no longer sense theposition magnet of the cart and, in turn, no longer generate outputsignals having measureable amplitudes. Accordingly, the magnetic sensorscan be used to determine absolute positions of carts on the track. It isdesirable to improve the aforementioned feedback system.

SUMMARY OF THE INVENTION

By configuring an encoder scale as a varying scale with successivelyincreasing or decreasing pitch, sensors in a travel path of the scalecan detect a phase difference to determine an absolute position of thescale for use in an industrial control system. Due to the successivelyincreasing or decreasing pitch, each sensor can detect successivelyincreasing or decreasing properties (such as magnetic fields) from thescale in a uniquely identifiable pattern. By taking the differencebetween readings of adjacent sensors, each sensor detecting propertiesof the scale, an absolute position of the scale between the sensors canbe determined.

As used herein, determination of an “absolute” position refers todetermining position information for a moving element in a systemdespite power being removed. Accordingly, with absolute encoders, theposition of the encoder (for providing the position of the movingelement) is available immediately upon applying power. Absolute positiondetermination and absolute encoders are distinct from “incremental”position determination and incremental encoders as known in the art.

The principle for feedback for the encoder system is analogous to aNonius or Vernier principle to determine absolute position. A Vernierscale is a visual aid that allows a user to measure more precisely thancould be done unaided when reading a uniformly divided straight orcircular measurement scale. The Vernier scale is a subsidiary scale thatindicates where a measurement lies in between two of the graduations ofa main scale. In this way, the encoder system is like a Vernier scale byusing a phase difference between two sensor angles to determine anabsolute position on a single track scale.

In one aspect, a single track absolute encoder scale could comprise a 40millimeter long element of a mover with gradually increasing ordecreasing magnet lengths. A phase difference between two magnetic fieldsensors, such as Anisotropic Magnetoresistance (AMR) sensors, TunnelMagneto Resistance (TMR) sensors and/or Hall effect sensors, spaced 20millimeters apart can be used to determine the absolute position of themover. Accordingly, sensor spacing can set a maximum encoder travellength, such as 20 millimeters in this case. For example, the encoderscale could have seven magnets totaling 40 millimeters in length,including: a first magnet that is 7.4 millimeters long; a second magnetthat is 6.6 millimeters long; a third magnet that is 6.0 millimeterslong; a fourth magnet that is 5.5 millimeters long; a fifth magnet thatis 5.1 millimeters long; a sixth magnet that is 4.8 millimeters long;and a seventh magnet that is 4.6 millimeters long. An absolute rotaryencoder version could comprise, for example, a six magnet,variable-pitch rotary magnetic encoder scale with 4,000 counts per 180°degrees, an air gap between magnetic sensors and an encoder scale ofabout 5 millimeters. Accordingly, the present invention may provide alow cost absolute encoder including a single increasing or decreasing(1× to 2×) pitch encoder scale that is twice the travel distance long,and an encoder read head including two sets of analog sensors placed athalf the travel distance apart.

In one aspect, the magnets can be permanent magnets made from aferromagnetic material that is magnetized to create its own persistentmagnetic field. The magnets could be, for example, bonded magnets.

Specifically then, one aspect of the present invention can provide anencoder system for position determination, including: an encoder scalehaving multiple magnets arranged adjacently to one another, in which amagnetic pole pair including a north pole and a south pole of eachmagnet is arranged oppositely to a magnetic pole pair including a northpole and a south pole of an adjacent magnet so that the north pole of amagnet is adjacent to the south pole of a neighboring magnet and thesouth pole of the magnet is adjacent to the north pole of theneighboring magnet; and multiple sensors arranged along a path, eachsensor being configured to detect a magnetic field produced from theencoder scale across a gap when the encoder scale is proximal to thesensor, in which the encoder scale and the sensors are configured tomove with respect to one another in a direction, and in which magnets ofthe encoder scale successively increase or decrease in size with a firstmagnet of the plurality of magnets being largest and a last magnet ofthe plurality of magnets being smallest. In other aspects, optical,capacitive or inductive scales could be used.

These and other objects, advantages and aspects of the invention willbecome apparent from the following description. The particular objectsand advantages described herein can apply to only some embodimentsfalling within the claims and thus do not define the scope of theinvention. In the description, reference is made to the accompanyingdrawings which form a part hereof, and in which there is shown apreferred embodiment of the invention. Such embodiment does notnecessarily represent the full scope of the invention and reference ismade, therefore, to the claims herein for interpreting the scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred exemplary embodiments of the invention are illustrated in theaccompanying drawings in which like reference numerals represent likeparts throughout, and in which:

FIG. 1 is an exemplar industrial control system including a track havingcurved and linear sections and multiple carts for moving objects alongthe track in accordance with an aspect of the invention;

FIG. 2 is a cross sectional view of a cart along the track taken alongline A-A of FIG. 1;

FIG. 3A is a detailed plan view of an encoder system for absoluteposition determination which could be used in the industrial controlsystem of FIG. 1;

FIG. 3B is a detailed side view of the encoder system of FIG. 3A;

FIG. 4 is an isometric view of a section of magnetic tape which could beused in the encoder system of FIG. 3A;

FIG. 5 is a graph illustrating profiles detected by sensorscorresponding to positions of an encoder scale for absolute positiondetermination in the encoder system of FIG. 3A;

FIG. 6 is an isometric view of a rotary encoder system for absoluteposition determination in accordance with an aspect of the invention;

FIG. 7 is an isometric view of an optical rotary encoder system forabsolute position determination in accordance with an aspect of theinvention.

DETAILED DESCRIPTION OF THE OF THE INVENTION

Referring now to FIG. 1, in accordance with an aspect of the invention,an exemplar industrial control system 10 includes a track 12 havingcurved sections 14 and linear sections 16. Multiple carts 18, such ascarts 18 a, 18 b and 18 c, can be provided for moving objects along thetrack 12 from one location to another for accomplishing various tasks inthe industrial control system 10. The track 12 can be connected to acontroller 20, which can include a processor executing a program storedin a non-transient medium, and which can communicate with a HumanMachine Interface (“HMI”) 22 for providing I/O, for carrying out variousaspects of the invention as will be described herein. It will beappreciated that the track 12, being flexibly capable of curved andlinear sections according to various geometries, can be configured toimplement a wide variety of paths and orientations as may be required inthe environment.

With additional reference to FIG. 2, a cross sectional view of a cart 18along the track 12, such as the cart 18 a, taken along line A-A of FIG.1, illustrates certain aspects of the system. The cart 18 can include aframe 30, which may be aluminum, supporting one or more rollers 32 incommunication with the track 12 for moving the cart 18 along the track12. To move the cart 18, a power winding 34 disposed along the track 12can be selectively energized to electromagnetically react with a powermagnet 36 affixed to the cart 18 to thereby move the cart 18. The cart18 can include a work area 38 which can be used to accomplish variousindustrial control functions for moving objects. For determining aposition of the cart 18 along the track 12, the system can implement anencoder system 40 including a mover portion 42 which may be part of thecart 18 and a stationary portion 44 provided along the track 12. Themover portion 42 can be arranged to continuously face the stationaryportion 44 across a gap 46, which could be preferably a 3 millimeter airgap, as the cart 18 moves along the track 12.

With additional reference to FIGS. 3A and 3B, detailed plan and sideviews of area 50, respectively, of the mover portion 42 facing thestationary portion 44 across the gap 46 is provided according to anaspect of the invention. The encoder system 40 for positiondetermination can include an encoder scale 52 and multiple sensors 54,such as sensors 54 a, 54 b and 54 c, each sensor having a uniqueidentification corresponding to a relative position in the system. Theencoder scale 52 can be attached to the mover portion 42. The sensors 54can be attached the stationary portion 44, such as via surface mountingto a Printed Circuit Board (PCB) 13, along the track 12, forming a path.The sensors 54 are preferably evenly spaced apart along the path. In oneaspect, the encoder scale 52 can comprise a rectangular plate that is 25millimeters long on a longer first side 55 a, which is generallydisposed in a direction of travel 56, 10 millimeters wide on a shortersecond side 55 b, which is generally transverse to the direction oftravel 56, and about 1 millimeter thick on a third side 55 c, which isperpendicular to the direction of travel 56. The sensors 54 can bespaced apart along the path, for example, by 20 millimeters, in thedirection of travel 56.

The encoder scale 52 can include multiple magnets 60 arranged adjacentlyto one another, such as magnets 60 a, 60 b, 60 c, 60 d, 60 e, 60 f and60 g. The magnets can be permanent magnets made from a ferromagneticmaterial that is magnetized to create its own persistent magnetic field.The magnets could be, for example, bonded magnets. Each of the magnets60 can comprise a magnetic pole pair between sides of the magnet forproducing a magnetic field, such as a north pole 64 and a south pole 66for each magnet, with one pole facing toward the stationary portion 44,and the other pole facing away from stationary portion 44 (see FIGS. 3Aand 3B). Accordingly, magnetic pole pairs of the magnets 60 can bearranged oppositely to one another so that the north pole 64 of a magnetis adjacent to the south pole 66 of a neighboring magnet and the southpole 66 of the magnet 60 is adjacent to the north pole 64 of theneighboring magnet.

For example, a north pole 64 of the first magnet 60 a can be arrangedadjacently to a south pole 66 of the second magnet 60 b; the south pole66 of the second magnet 60 b can be arranged adjacently to a north pole64 of the third magnet 60 c; the north pole 64 of the third magnet 60 ccan be arranged adjacently to a south pole 66 of the fourth magnet 60 d;the south pole 66 of the fourth magnet 60 d can be arranged adjacentlyto a north pole 64 of the fifth magnet 60 e; the north pole 64 of thefifth magnet 60 e can be arranged adjacently to a south pole 66 of thesixth magnet 60 f; and the south pole 66 of the sixth magnet 60 f can bearranged adjacently to a north pole 64 of the seventh magnet 60 g, eachof the aforementioned poles facing toward the stationary portion 44across the gap 46 (see FIGS. 3A or 3B). Also, a south pole 66 of thefirst magnet 60 a can be arranged adjacently to a north pole 64 of thesecond magnet 60 b; the north pole 64 of the second magnet 60 b can bearranged adjacently to a south pole 66 of the third magnet 60 c; thesouth pole 66 of the third magnet 60 c can be arranged adjacently to anorth pole 64 of the fourth magnet 60 d; the north pole 64 of the fourthmagnet 60 d can be arranged adjacently to a south pole 66 of the fifthmagnet 60 e; the south pole 66 of the fifth magnet 60 e can be arrangedadjacently to a north pole 64 of the sixth magnet 60 f; and the northpole 64 of the sixth magnet 60 f can be arranged adjacently to a southpole 66 of the seventh magnet 60 g, each of the aforementioned polesfacing away from the stationary portion 44 (see FIG. 3B).

With additional reference to FIG. 4, each magnet could comprise, forexample, a 1 millimeter thick section of magnetic tape 70, which can belayered over a 0.3 millimeter thick stainless steel carrier tape 72,which can be layered over a 0.13 millimeter thick adhesive tape 74,which can be affixed to the mover portion 42.

The encoder scale 52 and the sensors 54 are configured to move withrespect to one another in the direction of travel 56. In one aspect,such as in the industrial control system 10, the encoder scale 52 canmove with the mover portion 42 along the track 12 while the sensors 54remain stationary on the track 12. However, in other aspects, thesensors 54 can move while the encoder scale 52 remains stationary, suchas when one or more sensors are on a mover portion and multiple encoderscales are on a stationary portion, or the sensors 54 and the encoderscale 52 can each be configured to move with respect to one another.

The sensors 54 can be magnetic field sensors configured to detectmagnetic fields produced from the encoder scale 52 when the encoderscale 52 is proximal to the sensor 54 across the gap 46. In addition,each sensor 54 can be configured to indicate a magnetic field directionproduced from the encoder scale 52. The sensors 54 could comprise, forexample, Anisotropic Magnetoresistance (AMR) sensors, Tunnel MagnetoResistance (TMR) sensors and/or Hall effect sensors. The sensors 54 canbe arranged on the PCB 13 (see FIG. 3B) disposed along the track 12 withsensing elements of the sensors 54 arranged perpendicularly to the PCB13 and the direction of travel 56.

In accordance with an aspect of the invention, the magnets 60 (includingthe magnetic pole pairs of each) of the encoder scale 52 cansuccessively increase or decrease in size (or pitch) with a first magnetof the multiple magnets 60 being largest and a last magnet of themultiple magnets 60 being smallest. For example, the encoder scale 52could have seven magnets totaling 40 millimeters in length, including:the first magnet 60 a that is 7.4 millimeters in length (being a largestmagnet 60); the second magnet 60 b that is 6.6 millimeters in length(being successively smaller than the first magnet 60 a); the thirdmagnet 60 c that is 6.0 millimeters in length (being successivelysmaller than the second magnet 60 b); the fourth magnet 60 d that is 5.5millimeters in length (being successively smaller than the third magnet60 c); the fifth magnet 60 e that is 5.1 millimeters in length (beingsuccessively smaller than the fourth magnet 60 d); the sixth magnet 60 fthat is 4.8 millimeters in length (being successively smaller than thefifth magnet 60 e); and the last, seventh magnet 60 g that is 4.6millimeters in length (being a smallest magnet 60) (which may provide upto 1 micron resolution). A coarser scale (e.g., fewer magnets and/or alarger air gap) may result in lower/coarser resolution, whereas a finerscale (e.g., a smaller air gap) may result in higher/finer resolution.For example, a magnet scale varying from 3.6 to 1.8 mm, with an air gapof about 3 mm, may provide a resolution up to 0.5 microns. Byconfiguring an encoder scale as a set of oppositely arranged, adjacentmagnets 60 with successively increasing or decreasing pitch, sensors 54in the direction of travel 56 of the encoder scale 52 can detect phasedifferences to determine absolute positions of the encoder scale 52 foruse in an industrial control system such as the system 10. Inparticular, due to the successively increasing or decreasing pitch, eachsensor 54 can detect successively increasing or decreasing magneticfields from the encoder scale 52 in a uniquely identifiable pattern. Acontrol system communicating with the sensors 54, such as the controller20, can take the difference between readings of adjacent sensors 54 todetermine an absolute position of the encoder scale 52. This principleis analogous to a Nonius or Vernier principle to determine absoluteposition.

For example, with additional reference to the diagram of FIG. 5, as theencoder scale 52 moves along the track 12 in one direction, a first end81 of the encoder scale 52 can first encounter the third sensor 54 c ata first time “A.” Due to the large size of the first magnet 60 a, thethird sensor 54 c will correspondingly detect an angle (illustratedbetween 0 to 2π radians) having a long profile 84 a. Then, as theencoder scale 52 continues to move in the same direction, thesuccessively smaller second magnet 60 b will cause the third sensor 54 cto correspondingly detect an angle having a successively smaller profile84 b at a second time “B.” Then, as the encoder scale 52 continues tomove in the same direction, the successively smaller third magnet 60 cwill cause the third sensor 54 c to correspondingly detect an anglehaving a successively smaller profile 84 c at a third time “C.” Then, asthe encoder scale 52 continues to move in the same direction, thesuccessively smaller fourth magnet 60 d will cause the third sensor 54 cto correspondingly detect an angle having a successively smaller profile84 d at a fourth time “D.” This detection pattern can continue for eachof the magnets 60 of varying pitch as the encoder scale 52 moves pastthe third sensor 54 c from the first end 81 through the second end 83.

However, with the sensors 54 being spaced apart by a fixed distance,such as 20 millimeters, and with the length of the encoder scale in thedirection of the path being at least twice the fixed distance, such as40 millimeters, at least two neighboring sensors 54 can detect theencoder scale 52 with different patterns at any given time. For example,when the third sensor 54 c correspondingly detects the angle having theprofile 84 d at the fourth time “D,” the second sensor 54 b cancorrespondingly detect an angle having a long profile 84 a, caused bythe large size of the first magnet 60 a, spanning the fourth time “D”and a fifth time “E.” Then, when the third sensor 54 c correspondinglydetects the angle having the profile 84 e at the fifth time “E,” thesecond sensor 54 b can correspondingly detect an angle having asuccessively smaller profile 84 b, caused by the successively smallersize of the second magnet 60 b, spanning the fifth time “E” and a sixthtime “F.” This detection pattern can continue for each of the magnets 60of varying pitch as the encoder scale 52 moves past the second and thirdsensor 54 b and 54 c, respectively. Analogous to a Nonius or Vernierscale, a control system communicating with the sensors 54, such as thecontroller 20, can thereby determine an absolute position 86 of theencoder scale 52 by calculating a phase difference between neighboringsensors, such as a first absolute position 86 a of the encoder scale 52taken by calculating a phase difference between the second and thirdsensor 54 b and 54 c, respectively, beginning at the fourth time “D.”Moreover, the control system can thereby determine additionalcharacteristics with respect to the encoder scale 52 and the attachedmover portion 42, such as direction, velocity, acceleration, and thelike, based on the sensed measurements.

It should be appreciated that many variations of the invention can beimplemented for achieving various encoder systems. For example, althoughthe encoder scale 52 is illustrated as having seven magnets by way ofexample, it should be appreciated that greater or fewer magnets 60 canbe used within the scope of the invention. Also, it should beappreciated that many variations of the invention can not only beimplemented for straight and/or curve sections for independent cartsystems, but also for low cost short stroke linear encoder systems withabsolute position determination and/or low cost, 180 degree rotaryencoder systems with absolute position determination. Moreover, withadditional gears, a second encoder scale could be added to countrevolutions for implementing a multi-turn encoder system.

Referring now to FIG. 6, in another aspect of the invention, a rotaryencoder system for position determination can include an encoder scale152 and sensors 154, such as sensors 154 a and 154 b. The encoder scale152 can be attached to a rotating portion, such as a drive shaft, whiletwo or more sensors 154 (placed half the scale length apart or 180degrees apart for rotary encoders) can be attached to a stationaryportion, arranged proximal to the encoder scale 152 across a gap 146,which could be an air gap. The encoder scale 152 can include multiplemagnets 160 arranged adjacently to one another in a ring, such asmagnets 160 a, 160 b, 160 c, 160 d, 160 e and 160 f. The magnets can bepermanent magnets, such as bonded magnets, and could comprise sectionsof magnetic tape 70 (see FIG. 4). Each of the magnets 160 can comprise amagnetic pole pair between inner and outer sides of the magnet forproducing a magnetic field, such as a north pole 164 and a south pole166 for each magnet, with one pole facing an outer side of the ring,toward the sensors 154 when rotated past, and the other pole facing aninner side of the ring, away from the sensors 154. Magnetic pole pairsof the magnets 160 can be arranged oppositely to one another in thering, meeting at a ring junction 169 forming a closed loop.

For example, a south pole 166 of the first magnet 160 a can be arrangedadjacently to a north pole 164 of the second magnet 160 b; the northpole 164 of the second magnet 160 b can be arranged adjacently to asouth pole 166 of the third magnet 160 c; the south pole 166 of thethird magnet 160 c can be arranged adjacently to a north pole 164 of thefourth magnet 160 d; the north pole 164 of the fourth magnet 160 d canbe arranged adjacently to a south pole 166 of the fifth magnet 160 e;and the south pole 166 of the fifth magnet 160 e can be arrangedadjacently to a north pole 164 of the sixth magnet 160, each of theaforementioned poles facing an outer side of the ring. Also, a northpole 164 of the first magnet 160 a can be arranged adjacently to a southpole 166 of the second magnet 160 b; the south pole 166 of the secondmagnet 160 b can be arranged adjacently to a north pole 164 of the thirdmagnet 160 c; the north pole 164 of the third magnet 160 c can bearranged adjacently to a south pole 166 of the fourth magnet 160 d; thesouth pole 166 of the fourth magnet 160 d can be arranged adjacently toa north pole 164 of the fifth magnet 160 e; and the north pole 164 ofthe fifth magnet 160 e can be arranged adjacently to a south pole 166 ofthe sixth magnet 160 f, each of the aforementioned poles facing an innerside of the ring.

The encoder scale 152 and the sensors 154 are configured to move withrespect to one another in a rotary direction of travel, such as theencoder scale 152 rotating clockwise or counter-clockwise. The sensors154 can be magnetic field sensors configured to detect magnetic fieldsproduced from the encoder scale 152 based on the configuration of theencoder scale 152 that is proximal to the sensors 154 across the gap146. In addition, each sensor 154 can be configured to indicate amagnetic field direction produced from the encoder scale 152. Thesensors 154 could comprise, for example, AMR sensors, TMR sensors and/orHall effect sensors. The sensors 154 can be arranged on a PCB withsensing elements of the sensors 154 arranged perpendicularly to the PCBand the encoder scale 152.

In accordance with an aspect of the invention, the magnets 160(including the magnetic pole pairs of each) of the encoder scale 152 cansuccessively increase or decrease in size (or pitch) in the ring with afirst magnet of the multiple magnets 160 being largest and a last magnetof the multiple magnets 160 being smallest. For example, the encoderscale 52 could have six magnets in which the first magnet 160 a is alargest magnet; the second magnet 160 b is successively smaller than thefirst magnet 160 a; the third magnet 160 c is successively smaller thanthe second magnet 160 b; the fourth magnet 160 d is successively smallerthan the third magnet 160 c; the fifth magnet 160 e is successivelysmaller than the fourth magnet 160 d); and the last, sixth magnet 160 fis a smallest magnet. By configuring an encoder scale as a set ofoppositely arranged, adjacent magnets 160 with successively increasingor decreasing pitch in a ring, the sensors 154 can detect phasedifferences to determine absolute positions of the encoder scale 152. Inparticular, due to the successively increasing or decreasing pitch, eachsensor 154 can detect successively increasing or decreasing magneticfields from the encoder scale 152 in a uniquely identifiable pattern. Acontrol system communicating with the sensors 154, such as thecontroller 20, can take the difference between readings of adjacentsensors 154 to determine an absolute position of the encoder scale 152.This principle is analogous to a Nonius or Vernier principle todetermine absolute position.

Referring now to FIG. 7, in another aspect of the invention, an opticalencoder system for position determination implementing similarprinciples can include an optical encoder scale 252 and at least twosensors 255 arranged proximal to the encoder scale. The encoder scale252 can comprise a disk 268 having multiple holes 270 evenly spacedcircumferentially around an interior area. The sensors 255 can bearranged proximal to the encoder scale 252. Each sensor can comprise aphoto cell 256 and a light source 258. Each photo cell 256 can beconfigured to detect light 253 across a gap from the light source 258through holes 270 in the disk 268. Each photo cell 256 could include oneor more photo transistors, photo diodes or the like for capturing light.The encoder scale 252 and the sensors 255 can be configured to move withrespect to one another, such as the encoder scale 252 being attached toa rotating portion 290, such as a drive shaft, while the sensors 255 areattached to a stationary portion, arranged proximal to the encoder scale252 across a gap, which could be an air gap. The holes 270 of theencoder scale 252 successively increase or decrease in size with a firsthole 270 a being largest and a last hole 270 b being smallest and withthe first hole 270 a being arranged adjacently to the last hole 270 b inthe interior area. The holes 270 of the encoder scale 252 cansuccessively increase or decrease in size by a factor of two to one(2:1) from the first hole to the last hole.

Certain terminology is used herein for purposes of reference only, andthus is not intended to be limiting. For example, terms such as “upper,”“lower,” “above,” and “below” refer to directions in the drawings towhich reference is made. Terms such as “front,” “back,” “rear,”“bottom,” “side,” “left” and “right” describe the orientation ofportions of the component within a consistent but arbitrary frame ofreference which is made clear by reference to the text and theassociated drawings describing the component under discussion. Suchterminology may include the words specifically mentioned above,derivatives thereof, and words of similar import. Similarly, the terms“first,” “second” and other such numerical terms referring to structuresdo not imply a sequence or order unless clearly indicated by thecontext.

When introducing elements or features of the present disclosure and theexemplary embodiments, the articles “a,” “an,” “the” and “said” areintended to mean that there are one or more of such elements orfeatures. The terms “comprising,” “including” and “having” are intendedto be inclusive and mean that there may be additional elements orfeatures other than those specifically noted. It is further to beunderstood that the method steps, processes, and operations describedherein are not to be construed as necessarily requiring theirperformance in the particular order discussed or illustrated, unlessspecifically identified as an order of performance. It is also to beunderstood that additional or alternative steps may be employed.

It is specifically intended that the present invention not be limited tothe embodiments and illustrations contained herein and the claims shouldbe understood to include modified forms of those embodiments includingportions of the embodiments and combinations of elements of differentembodiments as coming within the scope of the following claims. All ofthe publications described herein including patents and non-patentpublications are hereby incorporated herein by reference in theirentireties.

What is claimed is:
 1. An encoder system, comprising: an encoder scale comprising first and second magnets, each magnet comprising north and south poles, wherein the north pole of the first magnet is arranged adjacently to the south pole of the second magnet and the south pole of the first magnet is arranged adjacently to the north pole of the second magnet; and a sensor arranged in proximity to the encoder scale across a gap, the sensor being configured to detect a magnetic field from the encoder scale, wherein the encoder scale and the sensor are configured to move with respect to one another in a direction of travel, and wherein the second magnet is smaller than the first magnet.
 2. The system of claim 1, wherein the encoder scale further comprises a third magnet arranged adjacently to the second magnet, wherein the north pole of the third magnet is arranged adjacently to the south pole of the second magnet and the south pole of the third magnet is arranged adjacently to the north pole of the second magnet.
 3. The system of claim 2, wherein the third magnet is smaller than the second magnet.
 4. The system of claim 1, wherein the encoder scale is attached to a cart and the sensor is attached to a track.
 5. The system of claim 4, wherein the track comprises linear and curved sections.
 6. The system of claim 1, wherein the encoder system is an absolute linear encoder.
 7. The system of claim 1, wherein the encoder system is an absolute 180 degree rotary encoder.
 8. The system of claim 1, wherein the sensor is one of a plurality of sensors, and further comprising a processor in communication with the plurality of sensors, wherein the processor executes a program stored in a non-transient medium to locate an absolute position of the encoder scale with respect to a sensor of the plurality of sensors.
 9. The system of claim 8, wherein the processor locates the absolute position of the encoder scale by calculating a phase difference between two sensors of the plurality of sensors.
 10. The system of claim 8, wherein the sensors are Anisotropic Magnetoresistance (AMR), Tunnel Magneto Resistance (TMR) or Hall effect sensors mounted to a Printed Circuit Board (PCB).
 11. The system of claim 1, wherein the sensor is one of a plurality of sensors with each sensor being spaced apart by a distance, and wherein a length of the encoder scale in the direction of travel is at least twice the distance.
 12. The system of claim 11, wherein the distance is at least 20 millimeters.
 13. The system of claim 11, wherein the first and second magnets comprise magnetic tape.
 14. A method for determining a position, comprising: providing an encoder scale comprising first and second magnets, each magnet comprising north and south poles, wherein the north pole of the first magnet is arranged adjacently to the south pole of the second magnet and the south pole of the first magnet is arranged adjacently to the north pole of the second magnet, wherein the second magnet is smaller than the first magnet; providing a sensor arranged in proximity to the encoder scale across a gap, the sensor being configured to detect a magnetic field from the encoder scale; and moving the encoder scale with respect to the sensor in a direction of travel.
 15. The method of claim 14, further comprising providing the encoder scale with a third magnet arranged adjacently to the second magnet, wherein the north pole of the third magnet is arranged adjacently to the south pole of the second magnet and the south pole of the third magnet is arranged adjacently to the north pole of the second magnet.
 16. The method of claim 15, wherein the third magnet is smaller than the second magnet.
 17. A rotary encoder system, comprising: an encoder scale comprising first and second magnets, each magnet comprising north and south poles, wherein the north pole of the first magnet is arranged adjacently to the south pole of the second magnet and the south pole of the first magnet is arranged adjacently to the north pole of the second magnet, wherein the first and second magnets are arranged in a ring; and a sensor arranged in proximity to the ring across a gap, the sensor being configured to detect a magnetic field from the encoder scale, wherein the encoder scale and the sensor are configured to move with respect to one another in a rotary direction of travel, and wherein the second magnet is smaller than the first magnet.
 18. The system of claim 17, wherein the encoder scale further comprises a third magnet arranged adjacently to the second magnet in the ring, wherein the north pole of the third magnet is arranged adjacently to the south pole of the second magnet and the south pole of the third magnet is arranged adjacently to the north pole of the second magnet.
 19. The system of claim 18, wherein the third magnet is smaller than the second magnet.
 20. The system of claim 17, wherein the encoder scale is attached to a drive shaft. 